Project Summary Regular exercise is a proven, powerful and cost-effective intervention for the treatment and secondary prevention of coronary artery disease. However, a detailed understanding of the fundamental cellular and molecular mechanisms that underlie exercise-induced cardioprotection are lacking, limiting the development of effective new therapeutic strategies for diseased patients. Despite recent advances in the appreciation of reactive oxygen species (ROS) as critical regulators of cell signaling, the details of the specific contributions of these molecules to physiologic signaling and functional adaptions in the vascular system remain to be elucidated. This is particularly true in the coronary microcirculation where studies determining the contributions of ROS in the control of blood flow are sparse. The proposed studies will utilize a combination of in vitro and in vivo approaches to determine how exercise-induced adaptations in ROS signaling affect vascular reactivity and coronary blood flow into both control and ischemic myocardium, an area that has been largely unexplored in the coronary circulation. The overarching hypothesis is that ROS play a critical and protective role in the exercise training-induced restoration of vasodilation responses in the coronary microcirculation and thereby enhances perfusion and contractile function of the at-risk myocardium. Aim 1 will determine exercise training- induced adaptations in ROS production in hearts subjected to chronic coronary artery occlusion. Aim 2 will determine the effects of exercise training on the expression and subcellular localization of candidate sources of ROS production and associated regulatory subunit proteins in microvascular endothelium of hearts subjected to chronic coronary artery occlusion. Aim 3 will identify the adaptations by which exercise training promotes downstream signaling pathway(s) for ROS-mediated dilation in arterioles isolated from hearts subjected to chronic coronary artery occlusion. Aim 4 will identify the signaling mechanisms by which exercise training enhances regional perfusion and myocardial contractile function at rest and during dobutamine-induced myocardial stress in hearts subjected to chronic coronary occlusion. These studies are of high impact since the knowledge gained will provide novel insight into the protective role of ROS in the cardiovascular system. The proposed studies will provide important new information with significant mechanistic insight into human ischemic heart disease and identify the role of ROS signaling in the control of coronary blood flow in health, disease, and exercise adaptation.